Have you ever noticed that your hair seems to grow quicker during the warm summer months? You’re not alone. Many people report that their hair appears to grow faster in the summer compared to the winter. But is this merely an observation, or is there scientific evidence behind this common belief? This article explores the relationship between seasonal changes and hair growth rates, examining what science has to say about whether hair truly grows faster in summer.
Understanding the Hair Growth Cycle
To understand how seasons might affect hair growth, we first need to understand how hair grows naturally.
The Four Phases of Hair Growth
Hair growth follows a predictable cycle with four distinct phases:
- Anagen (Growth Phase): This active growth phase lasts 2-7 years, during which hair cells divide rapidly and add to the hair shaft. About 85-90% of your scalp hairs are in this phase at any given time.
- Catagen (Transition Phase): A brief transitional phase lasting about 2 weeks, where hair growth slows and the hair follicle shrinks.
- Telogen (Resting Phase): This is a resting period lasting about 3 months where no growth occurs. Approximately 10-15% of hairs are in this phase at any time.
- Exogen (Shedding Phase): The final phase where old hairs are shed from the scalp, making way for new growth.
Average Hair Growth Rates
On average, human hair grows approximately 0.5 inches (1.25 cm) per month, or about 6 inches (15 cm) per year. However, this rate can vary based on factors including:
- Age
- Genetics
- Overall health
- Nutritional status
- Hormonal fluctuations
- Environmental conditions
- Season
Scientific Evidence: Does Hair Grow Faster in Summer?
The Landmark Sheffield Study
The most frequently cited research on seasonal hair growth comes from a study published in the British Journal of Dermatology in 1991 by Dr. Valerie Randall and colleagues. This study, conducted at the University of Sheffield, tracked hair growth parameters in 14 healthy Caucasian men over 18 months.
The researchers found that:
- The proportion of follicles in the anagen (growth) phase peaked in March at over 90%
- Hair shedding reached its highest point around August/September
- Beard growth was lowest in January and February
- Beard growth increased steadily from March to July, reaching a peak approximately 60% above winter levels
- Thigh hair showed a similar pattern, but with less pronounced differences
- No seasonal fluctuations were detected in finger or toenail growth
This study provides strong evidence that seasonal changes do influence hair growth patterns, with increased growth rates during late spring and summer months.
Additional Scientific Research
Subsequent studies have provided further insights:
- A 2009 study published in Dermatology found that women experienced increased hair shedding in the summer months, which aligns with the Sheffield study’s findings about telogen phase timing.
- Research on blood circulation indicates that warmer temperatures increase blood flow to the scalp, potentially delivering more nutrients to hair follicles during summer months.
- A study published in the Journal of Dermatological Science found that seasonal changes affect the molecular mechanisms controlling hair follicle cycling.
Why Hair May Grow Faster in Summer
Based on scientific research, there are several biological mechanisms that might explain why hair tends to grow faster during the summer months:
1. Increased Blood Circulation
Warmer temperatures cause blood vessels to dilate, increasing blood flow throughout the body, including the scalp. This enhanced circulation delivers more oxygen and nutrients to hair follicles, potentially boosting growth rates.
Research suggests this increased circulation can result in approximately 10% faster hair growth during the summer compared to the winter months.
2. Vitamin D and Sunlight Exposure
Increased sun exposure during summer leads to higher vitamin D production in the body. Vitamin D plays several important roles in hair growth:
- Helps create new hair follicles
- Activates cells within the hair shaft
- Wake up dormant follicles
Dr. Marisa Garshick, a board-certified dermatologist, explains: “Vitamin D plays a role in hair follicle cycling, and its deficiency has been linked to hair loss. The increased sun exposure during summer months can boost vitamin D levels, potentially supporting healthier hair growth.”
3. Hormonal Changes
Seasonal variations affect hormone levels, which in turn influence hair growth:
- Human growth hormone (HGH) production increases during summer months
- Melatonin levels change with varying daylight hours
- Testosterone fluctuates seasonally
These hormonal shifts may stimulate more follicles to enter the anagen phase during summer, increasing overall growth rates.
4. Evolutionary Perspective
From an evolutionary standpoint, some researchers suggest that humans, like other mammals, may have retained a biological mechanism that promotes increased hair growth during warmer months as protection against sun exposure and various environmental factors.
Measurable Differences in Seasonal Growth
How significant are these seasonal differences in hair growth? According to research:
- Summer growth rates can be 10-15% faster than winter rates
- The Sheffield study observed a 60% increase in beard growth from winter to summer
- Hair density measurements show approximately 5-7% more follicles in the anagen phase during late spring/early summer compared to winter
While these differences are measurable in scientific studies, they may not be dramatically noticeable to the casual observer in daily life.
Common Myths About Summer Hair Growth
Despite the scientific evidence supporting some seasonal variation in hair growth, several myths persist:
Myth 1: Sweating Stimulates Hair Growth
Reality: While sweating helps cleanse the scalp of buildup, there’s no scientific evidence that sweat itself stimulates hair follicles or promotes growth. Excessive sweating without proper cleansing can lead to scalp irritation and even inhibit healthy hair growth.
Myth 2: Hair Grows Significantly Faster in Summer
Reality: While research does support faster growth in summer, the difference is modest—approximately 10-15% faster than winter rates. This translates to only about 1-2 millimeters of additional growth per month, which may not be visibly noticeable.
Myth 3: Swimming Promotes Hair Growth
Reality: Swimming itself doesn’t directly affect hair growth rates. Exposure to chlorinated or salt water without proper protection can damage hair. However, increased physical activity and better circulation from swimming may indirectly support overall hair health.
Myth 4: Summer Hair Growth Is Just an Optical Illusion
Reality: This is partly a myth. While some people might perceive faster growth due to factors like increased humidity (which can make hair appear longer by reducing frizz), scientific studies confirm that actual biological growth rates do increase somewhat during summer months.
Optimizing Hair Growth Year-Round
Whether in summer or winter, there are several evidence-based strategies to maintain healthy hair growth:
Nutritional Support
- Protein: Hair is primarily made of protein (keratin), so adequate intake is essential
- Iron: Iron deficiency has been linked to hair loss, particularly in premenopausal women
- Vitamins: B vitamins (especially biotin), vitamins A, C, D, and E all support hair health
- Zinc and Selenium: These minerals play important roles in hair structure and growth
Scalp Care
- Regular cleansing keeps follicles clear of buildup
- Scalp massage: Improves blood circulation to follicles
- Protection from environmental damage: UV rays, pollution, and extreme temperatures
Summer-Specific Hair Care Tips
During the summer months, consider these strategies to protect your hair and potentially maximize growth:
- Sun protection: Use hats or UV-protective hair products to prevent damage
- Proper hydration: Drink plenty of water to support circulation and overall hair health
- Pre/post-swim care: Apply a protective layer before swimming and rinse thoroughly afterward
- Lightweight conditioning: Use appropriate products to prevent humidity-related frizz without weighing hair down
When to Seek Professional Help
Seasonal variations in hair growth are normal, but significant changes may warrant medical attention. Consult a dermatologist if you experience:
- Sudden or excessive hair loss
- Patchy hair loss
- Scalp irritation, pain, or scaling
- Hair thinning that doesn’t follow typical seasonal patterns
Dr. Robert M. Bernstein, Clinical Professor of Dermatology at Columbia University, advises: “While some seasonal shedding is normal, dramatic changes in hair density or growth patterns should be evaluated by a specialist to rule out underlying medical conditions.”
Conclusion
The scientific evidence suggests that hair does indeed grow somewhat faster during summer months—approximately 10-15% faster than in winter. This increase is primarily attributed to improved blood circulation, increased vitamin D production, and seasonal hormonal changes.
However, the difference is relatively modest and may not be dramatically noticeable in everyday life. Understanding these natural fluctuations can help you better manage your hair care routine and set realistic expectations for growth throughout the year.
Rather than focusing exclusively on seasonal changes, a comprehensive approach to hair health—including proper nutrition, protection from environmental damage, and appropriate hair care practices—remains the most effective strategy for maintaining optimal hair growth year-round.
FAQs About Seasonal Hair Growth
Does everyone’s hair grow faster in the summer?
While research indicates a general trend toward faster growth in summer months, individual responses vary. Factors such as genetics, overall health, and hair care practices also significantly influence growth rates.
Is the effect more noticeable with certain hair types?
Research hasn’t conclusively shown whether certain hair types experience more pronounced seasonal growth variations than others. However, people with naturally fast-growing hair may notice seasonal differences more readily.
Does hair color affect seasonal growth patterns?
There’s no strong scientific evidence suggesting that hair color influences how hair responds to seasonal changes in terms of growth rate.
How can I measure my hair’s growth rate to detect seasonal changes?
For accurate tracking, select a specific section of hair and measure from a fixed point on the scalp monthly. Consistent measurement techniques and timing are crucial for meaningful comparisons.
Do seasonal growth patterns differ between men and women?
Research suggests that both men and women experience similar seasonal patterns in hair growth, though hormonal differences may cause some variations in the magnitude of these effects.
References
- Randall, V. A., & Ebling, F. J. (1991). Seasonal changes in human hair growth. British Journal of Dermatology, 124(2), 146-151.
- Kunz, M., Seifert, B., & Trüeb, R. M. (2009). Seasonality of hair shedding in healthy women complaining of hair loss. Dermatology, 219(2), 105-110.
- Courtois, M., Loussouarn, G., Hourseau, C., & Grollier, J. F. (1996). Periodicity in the growth and shedding of hair. British Journal of Dermatology, 134(1), 47-54.
- Chen, C. C., & Chuong, C. M. (2012). Multi-layered environmental regulation on the homeostasis of stem cells: The saga of hair growth and alopecia. Journal of Dermatological Science, 66(1), 3-11.
- Hamblin, J. (2016). The truth about hair growth in summer. The Atlantic. Retrieved from https://www.theatlantic.com/health/archive/2016/07/does-hair-grow-faster-in-summer/490811/
